Feelingnojoy I would focus on finding your connection with your son first.
junbean gives great advice, it's spot on. Im not going to repeat what was said but could do, its all right. I work with children like your son.
You are focusing on the weed and 'making' him stop. Fact is, he's got to want to stop for that to successfully happen. The way to get him to understand why you want him to stop, is him caring about your opinion. By being authoritarian and judgmental, it will further cement to him that your opinions are irrelevent and dont matter.
When you say smoking weed every day, is this socially with friends? If so, that's not a concern in terms of how he's paying for it. They'll likely be sharing. (Which incidentally cements their connection in a way that his connection with you might be lacking).
As a parent, I'd continue to condone it, but not be judgmental about weed smoking. Don't make it easy or encourage it, but equally I wouldn't be sanctioning or punishing for the weed smoking in itself. I'll caveat that with, I would place a hard rule on no weed in the house but not for (for example) smelling of weed when coming home. Its about choosing your battles. You won't be able to make him stop just because you want him to, but you can place rules and boundaries around where the line is.
Regarding phone tracking, personally that's important to me with my teens (I know others disagree). But by sixth form, it comes with negotiating. Since I know my older teens could refuse if they wanted, the negotiation is that I agree not to comment on, judge or tell them off about their location, as long as the location is on. If you've been using Life360 as a metaphorical stick to beat him with, no wonder he refuses to have it on.